This Is How Much Water You Should Drink On a Plane

Depending on where you’re going, how long you’re traveling, and what kind of a plane you’re on.

Desert-like airplane cabins, a no-liquids TSA rule, and in-flight libations make dehydration a common condition for travelers. But in-the-skies hydration isn’t a math equation: There’s no specific catch-all for how much water you need to drink while flying, says Clayton T. Cowl, M.D., Chair of the Division of Preventive, Occupational, and Aerospace Medicine at the Mayo Clinic. (That's right, there's a chair of aerospace medicine at the Mayo Clinic.) That said, doctors and travel health organizations have some suggestions when it comes to filling up on H2O at 30,000 feet.

If you're on a long flight...

The Aerospace Medical Association suggests about eight ounces of water every hour you’re in the air. The longer the flight, however, the more hydration matters. You likely won’t get dehydrated from a three to four-hour flight, especially if you drink a bit of water during beverage service, says Peter Hackett, M.D., director of the Institute for Altitude Medicine.

Flying from Chicago to Bangalore—or even coast-to-coast? Aim to drink enough water so that you’re getting up to go every so often, says Dr. Cowl. This isn’t just about hydration: Hitting the restroom forces you to move, which keeps blood flowing in your legs, preventing against issues like deep vein thrombosis (DVT), blood clots in the legs.

If you're boozing...

Alcohol dehydrates your body on the cellular level, says Dr. Cowl. That’s one of the reasons The Aerospace Medical Association suggests limiting in-flight happy hours. Can’t pass up the pinot? An eight-ounce glass of water is probably sufficient to counteract the dehydrating effect from one glass of wine, says Hackett. (For reference, most plastic airline cups hold about nine ounces.)

If you're headed to a high-altitude destination...

Cold mountain air has its perks—but being hydrating is not one of them. Since humidity drops the higher up you are, you’ll lose fluids faster. But you don’t need to overdo it with water to fend off altitude sickness (too much water can actually dilute sodium levels in your blood, leaving you woozy or worse). An extra one, to one-and-a-half liters of water a day should be fine, says the Institute for Altitude Medicine.

If you're on a newer plane...

Cabin humidity usually teeters around 20 percent, says The Aerospace Medical Association. Other studies suggest it’s lower: closer to 10 percent. Regardless, filtered cabin air is usually cool and dry, says Dr. Cowl. “This air tends to pull moisture out of the system. Generally, you get more dehydrated in this type of an environment.”

So what about newer planes — like the Dreamliner 787 or the Airbus A350 — that boast cabin humidities around 25 percent? This might make for a more comfortable ride (read: less of that dry, scratchy feeling in your throat), but these planes don’t engineer out the need for water, says Dr. Cowl. “If the flight attendant comes by with a tray of water, it’s still good to have the water."